1. Field of the Invention
The present invention relates to a ceramic electronic device, such as a multilayer ceramic capacitor, and the production method, and particularly relates to a highly reliable ceramic electronic device having a temperature characteristic of a capacitance and low IR temperature dependency and the production method.
2. Description of the Related Art
A multilayer ceramic capacitor as an example of an electronic device is produced, for example, by co-firing a green chip obtained by alternately stacking ceramic green sheets formed by a predetermined dielectric ceramic composition and internal electrode layers having a predetermined pattern and making the result to be one body. The internal electrode layers of the multilayer ceramic capacitor are made to be one body with ceramic dielectrics by firing, so that it has been necessary to select a material which dose not react with the ceramic dielectrics. Therefore, it has been inevitable to use expensive precious metals, such as platinum and palladium, as the material for forming the internal electrode layers.
However, dielectric ceramic compositions, wherein inexpensive base metals, such as nickel and copper, can be used, have been developed in recent years and a large reduction of costs has been realized.
In recent years, multilayer ceramic capacitors have come to be used in a variety of electronic devices, such as an electronic control unit (ECU) installed in an engine room of a vehicle, a crank angle sensor and an Anti Lock Brake System (ABS) module. Since these electronic devices are for stable engine controlling, drive controlling and brake controlling, preferable temperature stability of the circuit is required.
Environments of using the electronic devices are expected to become about −20° C. or lower in winter in cold climates and about +130° C. or higher after the engine starts in summer. Recently, there is a tendency of reducing a wire harness for connecting the electronic device and a device to be controlled thereby and the electronic device may be provided outside of a vehicle, therefore, environments for the electronic devices have been getting more severe. Accordingly, there is a demand for an electronic device having an excellent temperature characteristic.
For the purpose of improving the temperature characteristic, for example, the patent article 1 (the Japanese Unexamined Patent Publication No. 2004-107200) discloses a dielectric ceramic composition comprising main crystal grains, interfacial grain boundary phases formed by the main crystal grains, and triple point grain boundary phases including M4R6O (SiO4)6 crystal (“M” is an alkaline metal and “R” is a rare earth).
Also, the patent article 2 (the Japanese Unexamined Patent Publication No. 2004-155649) discloses a dielectric ceramic comprising ABO3 (“A” is Ba, etc. and “B” is Ti, etc.) as a main component and also a rare earth element and Si, wherein at least a part of said rare earth element and said Si exist as a composite compound being different from the main component, ABO3.
However, in the patent articles 1 and 2, the temperature characteristic is compensated only up to 125° C. and, when used at a higher temperature (for example, 150° C.), there is a disadvantage that the capacitance is deteriorated. Moreover, there also have been disadvantages that dielectrics described in the articles have large IR temperature dependency, particularly, a decline of resistance (IR) when used at a high temperature is remarkable and the reliability is poor.